(a) Technical Field
The present invention relates to an organic-inorganic composite comprising bacteria and a transition metal oxide organic-inorganic composite.
(b) Background Art
For the last two decades, microsystem and nanotechnology have been developed rapidly having a wide spectrum of its applications in various fields of industry including automobile parts, electronic products, medical devices, thereby requiring light-weightness, compactness, high integration of the above products. Further, with the introduction of full-fledged era of nanotechonology, research has been conducted on nano-structured materials at a nanoscale level such as nanowire, nanobelt, nanorod, quantum dot, even advancing to nano robots to be used for the treatment of human diseases.
In fact, many researches have been focused on the synthesis of nano-structured inorganic materials because nano-structured inorganic materials exhibit unique characteristics, which have not been observed in micro-sized materials, and also revealed various excellent properties including more improved electromagnetic and optical properties, catalytic functions and high specific surface area than those with large capacity, thus being applicable to various fields. However, the conventional nano-structured inorganic materials, although synthesized using various materials and methods, have been highly limited in their forms produced [D. Chen et al., Cryst. Growth Des. 6 (2006) 247; U. A. Joshi et al., Inorg. Chem. 46 (2007) 3176; S. Nagamine et al., Mater. Lett. 61 (2007) 444].
Of methods attempted in synthesizing various forms of nano-structured inorganic materials, the method using a template is a representative method which enables to easily obtain various kinds of particular forms of nano-structured materials depending on the type of the template to be used. In particular, unique forms of nano-structured materials can be obtained by using various materials and structures including DNA molecules containing essential nucleotides for genes, polystyrene beads, anodizing aluminum oxides (AAO) [M. M. Tomczak et al., J. Am. Chem. Soc. 127 (2005) 12577; M. Yang et al., Adv. Funct. Mater. 15 (2005) 1523]. Further, there have been a few reports with the increase in synthesis of nano-structured inorganic materials using biomaterials such as proteins, viruses, bacteria, yeast, and fungi as templates [E. Dujardin et al., Nano Lett. 3 (2003) 413; T. Nomura et al., Mater. Lett. 62 (2008) 3727; N. C. Bigall et al., Angew. Chem. Int. Edit. 47 (2008) 7876; U.S. Patent Publication Nos. US20030068900; US20070287174; Japanese Patent Publication Nos. 2006-520317; 2007-517500]. Although the above method enables to obtain various forms of nano-structured inorganic materials by using various templates it also has drawbacks requiring a complex intermediate process such as surface treatment or addition and removal of a surfactant and also conducting the synthesis at high temperature to obtain inorganic materials with high crystallinity [F. Caruso, Top. Curr. Chem. 227 (2003) 145; H. Zhou et al., Microporous Mesoporous Mat. 100 (2007) 322; Y. Zhang et al., Mater. Lett. 62 (2008) 1435]. Especially, in case the biomaterials such as proteins, viruses, and bacteria are used as templates they may be broken or removed before the synthesis of inorganic materials thus not being able to obtain the materials with desired forms. Therefore, when synthesizing nano-structured inorganic materials using the above as templates it is necessary to provide a simplified process of synthesis as well as low temperature synthesis.
As mentioned above, nano-structured inorganic materials exhibit superior properties in many fields to be applicable to a variety of fields including nanoelectronics, photonics, catalysts, sensors, and energy storage. Therefore, in the present invention, nano-structured inorganic materials were manufactured using the above-mentioned template method; in particular, rod-shaped transition metal oxides and tube-shaped transition metal oxides were manufactured by using Bacillus bacteria with high electric potential as a template.
Notably, the problem of the method of the conventional synthesis with a complex process performed at high temperature (90-600° C.) is resolved in the present invention by attaching transition metal cations to negatively charged bacterial surface via electrostatic force without special surface treatment of the template, and performing reduction/spontaneous oxidation of the transition metal ions attached to the surface at room temperature by using a reducing agent. Further, not only rod-shaped but also tube-shaped one dimensional rods can be obtained by removing only the bacteria, which was used as a template, via calcination of rod-shaped nano-structured inorganic materials produced thereof. The nano-structured materials manufactured thereof can be applied to the manufacture of lithium ion secondary battery electrodes.
The above is due to the recent trend of achieving light-weightness, compactness, high density, and high integration in the field of portable electronic products such as laptop computers, mobile phones, and musical instruments. Further, with the recent growing concerns on safe environment, researches on the development of environment-friendly products such as electrical vehicles and hybrid vehicles have been performed actively thus requiring the development of technologies related to high capacity system and high power system of batteries used as electric sources for their locomotion.
Recently, various research developments using biomaterials as template and their applications in lithium secondary batteries have been reported [Published Korean Patent Application No. 2007-0097028; Published U.S. Patent Application No. US20080220333; Published Japanese Patent Application No. 2008-517070].
Unlike the primary batteries, which allow only a single use, secondary batteries in general are reusable by recharging. The primary batteries such as alkali batteries, mercury batteries, and manganese batteries with relatively high capacity, which are more commonly used, are not reusable and also not environment-friendly. Meanwhile, the secondary batteries such as lead storage batteries, nickel-cadmium batteries, nickel metal hydride batteries, lithium metal batteries, and lithium ion batteries are reusable, more energy-efficient than the primary batteries due to high voltage, environment-friendliness, while having high capacity and high energy density unlike the fuel cells, which have technical limitations due to their low energy density, thus being commercialized in various industrial fields.
Of these, the lithium ion batteries utilize the reversible insertion/deinsertion reaction occurring when lithium ions present in electrolytes, being lithium ionic conductor, move to either an anode active material or a cathode active material, where a lithium metal was first used as the anode active material. However, the research on this field has not been pursued further because of the drastic decrease in charge/discharge capacity due to the change in the shape of the electrode surface and the risk of explosion occurring in case there is a contact between the lithium metal dendrites generated from the negative electrode and the positive electrode.
In 1991, since SONY first used carbon as an anode active material and a lithium cobalt oxide as a cathode active material the term ‘lithium ion secondary battery’ has been used, and until now, anode active material based on reversible insertion/deinsertion reaction of carbon materials serves as a core part of the lithium ion secondary battery technology.
Of these, carbons such as hard carbons (nongraphitizable carbons), soft carbons and graphites are most widely used. Non-graphitic carbons such as hard carbons and soft carbons are not only capable of intercalating between layers in a layered structure but also capable of storing lithium ions via pores present inside carbons thus providing a much larger capacity than those of graphitic carbons, however, they have a drawback that they have a high irreversible capacity [R. Alcantara et al., J. Electrochem. Soc. 149 (2002) A201; J. R. Dahin et al., Carbon 35 (1997) 825-830].
Of carbon materials, graphite has been most widely commercialized. However, it also has drawbacks of having high cost, low capacity due to complex process, and difficulty in manufacturing high density electrodes in a planar form as is the case with natural graphite. Therefore, there was developed a new method of doping an atom such as boron to low price cokes-based artificial graphite and using thus prepared doped graphite as an anode active material [Japanese Patent Publication Hei 3-165463; Hei 3-245458; Hei 5-26680; Hei 9-63584].
However, the above carbon-based anode active material in general has a less theoretical capacity (372 mAh/g) and the commercialized capacity is known to be even less than the above. Further, it is not sufficient to meet the high capacity system required in portable electronic devices or electric vehicles because of the increase in the irreversibility of lithium secondary batteries caused by a subreaction occurring between an anode active material and an electrolyte solution during the charge/discharge process.
Accordingly, active researches have been performed on the anode active materials to replace the carbon-based materials, for example, transition metal oxides such as CuO, CoO, Fe2O3, NiO, and MnO2 which exhibit high capacity by alloying reactions to synthesize alloys with lithium such as Si, Ge, and Sn or conversion reaction between metals, instead of the conventional insertion/deinsertion process [W. J. Weydanz et al., J. Power Sources 237 81 (1999) 237-242; P. Poizot et al., Nature 407 (2000) 496].
Of these, in lithium secondary batteries, which are proceeded by the conversion reaction between metals, metal oxides undergo the charge/discharge process by a conversion reaction such as MxOy+2yLi⇄xM+yLi2O (M=transition metal), and also Li2O, which has long been considered not having electrochemical activity, expresses capacity while reacting irreversibly, therefore having an advantage of higher charge/discharge capacity than the insertion/deinsertion process. However, it has a drawback that the capacity rapidly decreases according to the increase in the number of cycles due to the aggregation among particles during the charge/discharge process. [R. Yang et al., Electrochem. Solid-State Lett. 7 (2004) A496-A499].
As a way to solve the above problem, there has been an attempt to use a low dimensional structure, in particular one dimension nanostructure such as nanowires, as an anode active material. However, this also has disadvantages that its manufacturing process is very complex and also a mass production is not possible [C. K. Chan et al., Nature Nanotech. 3 (2008) 31; C. K. Chan et al., Nano Lett. 8(1) (2008) 307; K. M. Shaju et al., Phys. Chem. Chem. Phys. 9 (2007) 1837].
From the above, it is apparent that there is a need for the development of a novel anode active material which has high capacity and enables to stably retain its high capacity during a long term charge/discharge process to replace the conventional carbon-based materials.